Loaded phantom-circuit.



- G. A. CAMPBELL & T. SHAW.

. LOADED PHANTOM 011mm. 1 APPLICATION FILE-BITE. 12, 1910. 4

- Patented Jan. 10, 1911.

3' SHEETS-.SHEET 1.

G. A. CAMPBELL & T. SHAW. v LOADED PHANTOM CIRCUIT.

APPLICATION FILED FEBflZ, 1910 Patented J 0, i911.

' 3 BE BHEET 2.

G. A. CAMPBELL & T. SHAW.

LOADED PHANTOM CIRCUIT.

APPLICATION TIL-ED PEB.12, 1910.

Patented Jan. 10, 1911.

3 BHBETSSHEET 3.

UNITED STATES PATENT OFFICE.

GEORGE A. CAMPBELL, F BROOKLYN, NEW YORK, AND THOMAS- snaw, OE AOKEN-SACK, NEW JERSEY, AssIeNORs TO AMERICAN TELEPHONE AND TELEGRAPH COMPANY,A CORPORATION OF n w YOR LOADED PHANTOM-CIRCUIT.

Application filed February 12, 1910. Serial No. 543,543.

To all whom it may concern:

Be it known that we, GEORGE A. CAMP- BELL and THOMAS SHAW, residing atBrook- 1 lyn and at Hackensack, respectively, in the counties of Kingsand Bergen, respectively, and States of New York and New Jensey,respectively, have invented certain Improyements in LoadedPhantom-Circuits, bf-

. sirable to combine two or more transmittin circuits to form a third,or, as it is terme in telephony, phantom circuit. @This is commonlyeffected by em loying 'in 'parallel the two limbs of a meta lic circuitto furnish each side of the phantom, the impulses generated in either ofthe original or physical circuits and in the combined or phantom circuitbeing caused to act only upon their respective receiving instruments bymeans of a differential repeating coil in a manner well known. lVhilethe loading coils for the physical circuits may be so organized thatthey provide therein the necessary inductance without greatly increasingthe effective resistance or other working characteristics of thephantom, they are also without appreciable effect upon the inductance ofsaid phantom. Therefore, if it is desired to also load the lattercircuit other means must be resorted to, and tofurnish such means is thepurpose of this invention. In the accompanying drawings, in whichsimilar characters of reference are applied to like parts throughout theseveral views: Figure 1 is a diagram showing phantomed loaded circuits,with the phantom itself loaded in accordance with our invention; Fig. 2is an enlarged diagram representing one of the hantom loading coils;Fig. 3 illustrates diagrammatically the distribution of admittances in acoil; and Fig. 4 is a view similar to Fig. 1-illustrating a modification0f the circuit.

Referring particularly to Fig. 1, the characters L and L designate,respectively, the opposite limbs of two metallic circuit telephone linesT and T each having terminal stations A, A. Near the extremities of bothllnes are the usual simplex're'peating Specification of Letters Patent.Patented J an. 10, 1911.

coils C, to the center of one wlndin of each of which is joined aconductor which continues to stations A the phantom circuit furnished bythe pairs of conductors L, L

in parallel. Current from batteries B is supplied to the physical andphantom circuits through repeating coils C". In both of the lines T, Tare included loading coils D, there being a sufficient number tointroduce the, required amount of inductance. Each coil may comprise aring-sha ed core of iron about which are windings or both sides of theline, each of said windings consisting of two sections of conductorwhich together encircle the entire core, there being a section of eachwinding upon each half core 10 10*.

Referring to either of the physical circuits, upon the core section 10is a winding section 12 for the conductor L of the line,

and over the core section 10" is a winding section 12 while the lineconductor L includes opposite windings 13 and 13". -To render the coilsymmetrical in the relation of its windings to one another and to thecore, the sections are of approximately equal impedance andthoseincluded in the same conductor are placed alternately directly aboutthecore and outside the sections of the companion winding, The windingsare of such length and direction, and the sec-' tions are so connected,that the desired inductance is introduced into each side of the physicalcircuit, the effective resistance being about the same as in thestandard loading coil, and it will be evident that a very perfectbalancemay be maintained between the windings. WVhen the windings are inparallel and exert-ing an opposing influence there is but little energywasted in magnetic leakage, and the effective resistance imposed uponthe phantom is slight. The inductance of the opposing windings isnegligible,"

therefore the phantom circuit is not loaded.

Cotiperatin with both the physical circuits are loa ing coils E for thephantom, but one of which is here illustrated, their number beingcontrolled by the inductance required to satisfactorily diminish theattenuation of current waves therein. Each 'upon'the coresection 16 arewindinggseccoil has a core preferably in the form of a ring consistingof a bundle of iron wire furnishing quarter sections 16, 16; 16 and 16,which are ordinarily parts of a con- ''tinuous rin in which case theterm section, woul refer merely to the portion of the core upon whichthe windings are placed. In this, the preferred. form of our invention,the core is common to windings included in the conductors L and L ofboth tions 17 and 18* of conductors L and of said line.. Similarly, overthe core sect'ons l6 and16 are winding sections 19, 20 and 20 and19 5fconductors L and L respectively, of the line T These coil sections areso woundand connected that when they are in parallel, as is thecase ineither side of the phantom circuit, their mutual inductance increasestheir self inductance; and with these two parallel sides joined inseries to complete the phantom, their mutual inductances are also added,these together giving the loading effect. This should'be secured withoutthe introduction of material transmission losses into the physicalcircuits and with comparative freedom from cross talk between thephantom and physical circuits and between such component circuits. Thewinding sections are therefore made of equal impedance'and aresymmetrically arranged upon the core sections. This may be seen mostclearly in Fig. 2 of the drawings, where, for convenience inillustration, the windings appear outside the core instead ofsurrounding and threaded through it, as is actually the case and as isrepresented in Fig. 1. It will be seen that winding sections 17 and 17encircle insulating material 21 covering the quarter sections 16 and 16of the core, with winding sections 19 and 19 similarly placed upon thecore sections 16 and 16; while the other winding sec tions in each casesurround a section included in the associated conductor of the line pairand being separated therefrom by insulation 22. Therefore, the windingsbelonging to the conductors of each line are concentrically arrangedthroughout, with their sections alternating in regard to their distancefrom the core. In each pair of concentric sections the current for thephysical circuits through each pair of conductors L, L in series travelsabout the core in opposite directions, and, as the number of turns andthe impedance of these sections are substantially the same, themagnetomotive forces which they produce will tend smear to neutralizeone another. As a result of this, there will be little leakage of linesof force into such unlaminated metal objects as the case 23, whichcustomarily incloses the coils, and only slight energy loss appearing aseffective resistance in the physical cir- V cuits. The only loadingeffect which the phantom coils will have upon the physical circuits willbe what may arise from these trifling losses, the mutual inductancefailing to exactly balance the self inductance.

Considering the passage of current for the phantom circuit through thepairs of conductors L, L in parallel, this will be in the same directionabout the core in all the winding sections; and, since these sectionscover the entire core and are symmetrical as to impedance and position,there will be practically no'external field or leakage from the .coilsand no expenditure of energy thereby. In addition to the substantialequality and symmetry between the impedances of the winding sections,both with re spect to the windings forming each side of the phantom andthe windings not associated with the same side of the phantom, thesections are so arranged that the outer layers, or those in proximity toother sections and tothe core and'case, are at substantially the samepotential as similarly located sections to and frbm which there might bea transfer of current by electrostatic induct-ion. This symmetricaldistribution of the direct admittances is clearly shown in Fig. 3 of thedrawings, taken in connection with Fig. 2, and requires no furtherexplanation. As a consequence of all these features of symmetry andbalancethe crosstalk between the phantom and its physical circuits andbetween such physical circuits is negligible.

In a system loaded in accordance with I this invention by coils havingtheusual cores, and with each line windingconsisting of about 163 innerturns of No. 17 B. & S. and about 163 outer turns of No. 16 B. & S.double cotton-covered copper conductor through which an alternatingcurrent of 800 m'icroamperes at 800 periods per second flows, each coilwas found to add to the phantom an inductance of 0.102 of a henry andeffective resistance of 3.35 ohms, while the two physical circuits eachreceived inductances of 718 microhenries and 1.72 ohms resistance, thelatter value being 0.08 of an ohm more than the corresponding directcurrent resistance.

Although the invention has been described in connection with a phantomcircuit made up of loaded lines, it will be evident that it is equallyapplicable to lines without loading coils.

In Fig. 4 is illustrated a modification of the invention. Here the coilsD of each of core.

set forth, but in the loading coils F for the phantom, the four windingsfor the two sides, instead of being upon a common core as in the coil E,are separated, the windings for each line pair having an individualSimilarly to the coils D, and for the purpose of reducing the magneticleakage and consequent transmission losses, the winding for eachconductor is preferably in sections and surrounds the entire core, beingsituated alternately inside and out; side the other winding sections. Inthis case, however, the sections are so joined as to add the mutualinductances of the windings to the self-inductance for the currents inthe phantom passing in the same direction through the parallel lineconductors. This may be accomplished by reversing the connections of thewinding for one lineconductor. Though this arrangement provides for thedesired loading of the phantom, it increases the number of coils whichit is necessary to use, introduces an additional resistance into thephysical circuits and is liable to cause cross talk. 7

We claim:

1. In a system for the transmission of electrical signals, a pluralityof transmitting circuits combined to form opposite sides of another orphantom circuit, and inductances included in, each side of the phantomcircuit and serving to diminish the attenua-' tion of the signahngimpulses therein.

2. In a system for the transmission of electrical signals, a pluralityof transmit ting circuits combinedto form opposite sides of another orphantom circuit, loading coils included in the first-named circuits,andmeans'for loadingthe phantom circuit independently of the loadingcoils of the component circuits.

Two telephone lines combined to fur- IllSll by the conductors of each inparallel opposite sides of a phantom circuit, and an' inductance in eachconductor of both lines, each inductance being associated in inductiverelation to the inductance in the companionconductor of the line andbein so connected that their mutual effect is a ded to theself-inductance. I

4'. In an electrical sig'nalingsyst'em, two line circuits associated to,furnish a third or phantom circuit, and a loading coil for thephantomfcircuit'having a winding included in each line conductor and acore common to all of said windings.

5. In an electrical si aling system, two line circuits associated tofurnish-a third or phantom circuit, and a loadin coil for the phantomcircuit having a win ing included in each line conductorand a corecommon to all of said windings, the windings for the two lines beingupon different sections of the core.

6. The combination with two,telephone lines, of means for formin aphantom circuit therefrom, and a loa ing .coil for the phantom circultcomprising a windin cluded in each side of the component ines, each ofsaid windings being divided into sections situated concentrically withrespect to the sect-ions of the other wlnding belong ing to thesame'line.

7. The combination with two telephone lines, of means for formin aphantom cmcuit therefrom, and a loa ing coil for the sections of thecore.

9. In a telephone system, two line circuits associated to furnishaphantom circuit, and a loading coil for the phantom circuit com-,

prising sectional windings included in both component lines, theadmittances'between each sectional winding and the other elements of thecoil being symmetrically d stributed.

In testimony whereof, we have signed our namesto this specification inthe presence of two subscribing witnesses, this twenty eighth day ofJanuary, 1910.

GEORGE A. CAMPBELL.

. THOMAS SHAW.

Witnesses:

W. M. GOULD,

FRANK B. J Ewn'rr.

